1. Field of the Invention
The present invention relates to a magnetic disk device for recording/reproducing information by means of a magnetic recording disk, and more particularly, to a head positioning mechanism which enables to enhance the positioning precision and to execute high speed seek.
2. Description of the Prior Art
In a prior magnetic disk device, positioning mechanism is utilized for magnetically writing information or reading recorded information, by moving a head in the radial direction along the concentric tracks recorded on the disk surface.
As one prior positioning mechanism for magnetic disk device one may mention a mechanism such as disclosed in Japanese Pat. No. 53-123911. This mechanism is composed of a carriage which supports the head, a guiding mechanism for giving parallel motion to the carriage, a pulley which is fixed to the rotation axis of a stepping motor and is driver stepwise from one angular position to the next angular position, and a nonstretchable flexible band whose mid section is wound and fixed to the pulley and whose both ends extend from the pulley to the carriage to be fixed there.
The above positioning mechanism operates as follows. Namely, when the stepping motor rotates for a predetermined angle, the pulley is rotated via the rotation axis by a predetermined angle, and one end of the flexible band is wound in around the pulley while the other end is pulled out. Then, the carriage is moved a linear distance which is proportional to the rotation angle of the pulley. In this way, the rotational motion of the pulley is converted to a linear motion of the carriage and the head is shifted stepwise in the radial direction crossing the concentric tracks on the magnetic disk plate, enabling to write information magnetically or read information recorded.
Now, the separation between tracks on the magnetic disk plate of this kind is on the order of 0.070-0.035 mm. Moreover, the time for moving the head from one track to the next is generally on the order of 3 milliseconds. The function of the positioning mechanism of the head is to move the head from one information track to the next information track in a shortest possible time.
However, the flexible band tends to create a slack with decrease in tension in the course of time, giving rise to a possibility of making exact positioning difficult. To avoid this, in a prior device there is installed a leaf spring between one end of the band and the carriage to provide a constant tension to the band. On the other hand, installation of the leaf spring gives rise to a disadvantage of generating a transient vibration when positioning is attempted by driving the stepping motor. Since the transient vibration lasts for such a long time as 50- 100 milliseconds, however, it leads to an increase in the seek time.
For this reason, in the above prior device, the inner circumferential surface of the opening in the collar plate which is fixed to the cover side is arranged to make a frictional contact with the armature axis of the stepping motor to effectively damp the transient vibration. However, in such a construction the friction between the armature axis and the collar plate becomes a load to the stepping motor such that there occurs a fear of aggravating the precision of positioning.
In contrast to the above, there exists also a device in which a damping element which utilizes the viscous resistance of fluid is attached to the armature axis for damping the transient vibration in order to alleviate the possibility of creating a load to the stepping motor. In this case, however, there is a possibility that the device will have to be made large in size.
Further, there exists another device in which the transient vibration is attempted to be reduced by electrically devising the driving of the stepping motor. However, such a device is unable to respond to the changes in the characteristics of the stepping motor so that there remains a fear that the design freedom may have to be sacrificed.